The invention concerns a camera for recording the topography of a specimen surface by generation of a Moire image with the aid of an object grid and a reference grid.
Moire processes are based on optically superposing two regular structures, such as line grids with grid constants of approximately equal size. The object grid which is applied or projected on the specimen is reproduced on a reference grid. The deformations of the object grid due to the topographic properties produce in the plane of the reference grid characteristic Moire lines.
From the IBM technical disclosure bulletin Vol. 25, No. 1, pages 357-358 (1982) it is known to reproduce the object grid contained on the specimen on a physical grid. The Moire lines created in this focal plane are recorded with the aid of a second projection by a CCD receiver camera. This second projection of Moire lines could be effected also by any other camera or on a photographic film.
The second projection is associated with considerable intensity losses, which requires a very high luminous intensity on the object. Especially with large-area specimens this is very difficult or expensive to accomplish, so that the prior art permits only small-area specimens or a low resolution.
A way out is constituted by the direct use of a CCD image sensor as a reference grid. The line or column structure of the sensor matrix can be used directly as the grid structure of a reference grid. While the resulting Moire images are not associated with intensity losses, so that a large specimen surface can be viewed, they nonetheless permit only a low resolution caused by the low number of lines/columns in the case of CCD image sensors. Such CCD sensors enable several hundred lines. While a combination of several CCD image sensors increases the line number of the reference grid, such requires a technically considerably more expensive and slower readout process of the obtained image.
Based on this prior art, the problem underlying the invention is to provide a camera of the initially mentioned type which has a high resolution and a large coverage.